Synthesis and Antifungal Study of Some Acetophenone Oximes and Their Terphthaloyl Oxime Esters

Acetophenone oximes 1 – 5 along with their terphthaloyl oxime esters 6 – 10 have been synthesized in moderate to good yields. Only one oxime was formed in as E/Z two isomers in a ratio of (8:1). These resulting oxime derivatives were involved in an antifungal screening against the Aspergillus niger at concentration of 30 ppm. Two commercially available antifungal agents, clorotimazole and daktarin, were employed as references at the same concentration, 30 ppm. The antifungal results for the oxime derivatives 1 – 10 showed inhibitory levels ranging from 38% to 100%, whereas the antifungal potentials for the two references were found to be ~ 63% and 68% for clorotimazole and daktarin respectively.


Instrumentation
Melting points were measured on a Barnstead electrothermal IA 9100. 1 HNMR spectrum was recorded on a JEOL ECA-500 II spectrometer. Residual proton signal from the deuteriated solvent was used as reference [DMSO ( 1 H, 2.50 ppm), whereas coupling constants were measured in hertz (Hz)]. Infrared spectrum was recorded on Jasco FT/IR-4100 Fourier transform infrared spectrometer. Mass spectrum was recorded on a Shimadzu Qp-2010 Plus. Antifungal study was conducted using petri dishes 9.0 cm.

General Procedures for The Synthesis of acetophenone oximes 1 -5:
A literature procedure [1] was adapted towards the synthesis of the desired oxime. Solution of hydroxylamine hydrochloride (1.08 mmol in 10 cm 3 of distilled water) and a solution of potassium hydroxide (0.80 mmol in 5 cm 3 of distilled water) were placed in a round-bottomed flask and stirred at room temperature. Acetophenone (1 mmol) was then added while stirring and the reaction mixture was refluxed. At the start of boiling, small amounts of ethanol (5 cm 3 ) were added from time to time to reaction mixture through the condenser until the boiling solution becomes clear. The reaction was left under reflux for further an hour after which the reaction vessel was allowed to cool gradually to room temperature. The pH of the reaction mixture was measured and found as expected to be acidic. A solution of 1N KOH was added to the reaction mixture until the solution became neutral. The reaction mixture was then refluxed for further 30 min, cooled to room temperature. The pH was measured and found to be still acidic. Addition of 1N KOH solution was required and the reaction mixture was refluxed for another 10 min, cooled, pH was measured and found to be neutral. The reaction mixture was transferred into a beaker containing ice-water (100 cm 3 ), the acetophenone oxime derivative was precipitated rapidly, filtered, washed with cold water (3 × 10 cm 3 ) and air dried to give the desired compound. The product was recrystallized from diethyl ether. Acetophenone

Synthesis of Acetophenone Oximes 1 -5
A mixture of acetophenone derivative and solution of hydroxylamine hydrochloride in the presence of potassium hydroxide was refluxed for 30 to 45 min. The corresponding acetophenone oximes were obtained as solid materials in moderate to good yields (Scheme 1).

Scheme-1. Synthesis of acetophenone oximes 1 -5
The spectroscopic analysis for the resulting compounds revealed the formation of the acetophenone oximes 1 -5. The IR data showed the absorption of the (OH) and the (C=N) groups at the expense of the carbonyl group (C=O) of the acetophenone derivative. The mass spectrometer gave the expected molecular ion masses along with the fragmentation patterns for all acetophenone oximes 1 -5. The 1 HNMR also confirmed the formation of all oximes 1 -5. Except the acetophenone oxime 1, which was obtained in two isomeric forms E/Z in ratio of about (8:1), the other acetophenone oximes 2 -5 were obtained as single isomers (Fig 1) [12].

Synthesis of the Bridged Terphthaloyl Acetophenone Oxime Esters 6 -10
The synthesis of the oxime esters 6 -10 was carried out through a n esterification reaction between the acetophenone oxime derivative and terphthaloyl chloride in the ratio of (2:1 mole/mole) under mild basic conditions at 0 °C to room temperature. The desired terphthaloyl oxime esters 6 -10 were formed in moderate yields as solid materials (Scheme 2).

Scheme-2. Synthesis of oxime esters 6 -10
The IR spectroscopic data revealed the disappearance of the oxime hydroxyl group and the formation of the ester groups (COO) as strong absorption bands for the entire oxime esters 6 -10. The 1 HNMR data of the oxime ester 6 confirmed the formation of these esters as all expected chemical shifts for all different protons appeared on the spectrum and the disappearance of the oxime hydroxyl proton of the starting oximes. The mass spectrometer provided additional evidence on the formation of the oxime esters 6 -10. The molecular ion masses were observed at 400, 428, 432, 430 and 490 m/z along with other molecular fragments for the oxime esters 6 -10 respectively, which were in a line with the expected theoretical fragmentation patterns.
The oxime 1 showed an excellent inhibitory level against the A. niger reaching 100%. However, its corresponding terphthaloyl ester 6 showed the lowest inhibitory level of all oxime derivatives under study, which was found to be 38%. The 4-methylacetophenone oxime 2 and its corresponding terphthaloyl ester 7, however, showed totally different results, recording 64% and 100% of inhibitory level respectively ( Table 1). The 4hydroxyacetophenone oxime 3 and its corresponding ester 8 followed similar behavior to that was recorded for the oxime 1 and the acetophenone terephthaloyl ester 6 ( Table 1). Table-1. The inhibitory levels of the acetophenone oxime derivatives 1 -10 at concentration of (30 ppm) against A. niger using two commercially available antifungal agents clorotimazole and daktarin as references. Note that the two references showed inhibitory levels matching ~ 63% and 68% respectively
Most of the oxime derivatives being synthesized throughout this study showed inhibitory levels better than the two references. Three of the synthesized oxime derivatives showed excellent levels of inhibition reaching 100%. Such high level of inhibition never allowed the A. niger to grow (Fig. 2).

Conclusion
Acetophenone oximes 1 -5 along with their terphthaloyl oxime esters 6 -10 have been synthesized in moderate to good yields. Only the acetophenone oxime 1 was formed in a mixture of E/Z isomers in a ratio of (8:1). The antimicrobial properties of these oxime derivatives were investigated against the Aspergillus niger at a concentration of 30 ppm. The commercially available antifungal agents, clorotimazole and daktarin, were used as references. The obtained results of the antifungal study for the oxime derivatives 1 -10 showed levels of inhibition ranging from 38% to 100%, whereas the antifungal effects for the two references were found to be ~ 63% and 68% for clorotimazole and daktarin respectively. Two oximes 1 and 3 along with the 4-methylacetophenone ester 7 showed the maximum levels of inhibition matching 100% inhibition. However, the oxime ester 6 showed the lowest inhibitory level (38%). Generally, the oximes showed higher inhibitory levels than those recorded for either their corresponding terphthaloyl esters and the commercially available two antifungal agents, clorotimazole and daktarin.